Water supply, sewerage, gas, electric power and communication networks are established all over urban areas, and manholes are provided for maintenance of the networks. It is difficult to observe the interior of a manhole from the ground, and therefore an operator opens the manhole lid in order to observe the interior of the manhole. Since the operational load for observing the interior of a manhole is high, the interior of a manhole is not always observed every time.
Although the combined system sewerage or the rainwater sewerage network prevents submergence of roads by quickly guiding rainwater that flows from roads at the time of rainfall to the sewage treatment plant, when the amount of rainfall is larger than the amount that may be treated in a short time, damage, such as submergence and inundation of a road, will occur. In recent years, localized torrential rain occurs frequently and countermeasures against the rain become more and more important. When the amount of rainfall is larger than the amount that may be treated, first, a large amount of rainwater flows into the conduit from the street rain inlet and the manhole, then the water level of the conduit and the manhole rises, and finally the water overflows from the manhole lid. Conventionally, the possibility of inundation and the degree of inundation can be predicted based on the amount of rainfall, and an advisory and a warning are issued to each area. However, it is desirable to observe the actual condition within the manhole in order to accurately observe the condition. However, in such a condition, since it is not easy to observe the condition within the manhole while ensuring the safety of an operator, a large amount water flows in the manhole and it is difficult for an operator to actually open the manhole lid and check the condition inside the manhole, and therefore the interior of the condition within the manhole is not observed.
It has been proposed to arrange various sensors within the manhole and to collect information on the manhole. It is desirable to arrange a large number of sensors and to collect detection data thereof, in order to observe the condition within the manhole. However, it is expensive in order to arrange a large number of sensors, and to construct and maintain a sensor system for collecting detection data from the large number of arranged sensors.
It has been proposed to provide a measurement device (sensor module) having a wireless communication device including an antenna in the manhole lid and to collect detection data of the sensor module by wireless communication.
In general, the combined system manhole lid and the rainfall manhole lid have holes to release overflowed water onto a road when water overflows within the manhole. Patent Document 1 discloses a sensor module having a wireless communication device, which may be installed in the hole or which may be installed only by performing simple processing around the hole of the manhole lid. Although it is desirable that a power source is provided in order for the sensor module to perform the detection operation and to transmit detection data by wireless communication, Patent Document 1 does not at all disclose a power source for the sensor module.
Patent Document 2 discloses a sensor module that is installed in the manhole lid and which performs wireless communication by using a space within the sewage conduit. Patent Document 2 discloses a power source for the sensor module including a battery and wind power generation device or a battery and solar power generation device. However, Patent Document 2 does not disclose a structure to install the sensor module in the manhole lid or an attachment structure with a wireless communication device that is arranged at the position of the sewage conduit to the manhole lid.
Although the sensor module disclosed in Patent Document 2 mounts a battery, the battery has a lifetime, and therefore the operation for exchanging batteries is a big problem. Normally, a manhole is opened for several years, and therefore the operation for exchanging batteries is difficult. Patent Document 2 describes usage of solar power generation or wind power generation. However, the surface of a manhole has bumps and dips for preventing slip, and it is difficult to install the solar battery, and the solar battery is apt to become stained soon, and therefore the solar battery is not actually effective. Further, in general, the distance between the manhole lid and the position of the top of the sewage conduit is quite long. Therefore, in actuality, the wireless communication device and the wind power generation device are arranged on the top of the sewage conduit and the rest of the sensor module is arranged in the manhole lid, and the rest connects with the wind power generation device. However, Patent Document 2 does disclose a connection structure of the arrangement and an attachment structure of the sensor module to the manhole lid. When such a connection structure is actually implementing, it is predicted that the sensor module increases in size. Therefore, it is difficult to install the sensor module of Patent Document 2 by using the already-existing hole of a manhole lid as described in Patent Document 1.
Further, although the wind power generation device has a mechanical mechanism including a rotating system, the environment within such a manhole of sewage is a poor environment in which the concentration of a corrosive gas, such as hydrogen sulfide, is high, and therefore it is difficult to maintain the operation state of the mechanical device having a rotating system for a long period of time.
As above, in order to take effective countermeasures by observing the condition within a manhole, it is desirable to arrange a large number of sensor modules in the manhole and to collect data. Therefore, it is desired that the sensor module be easily installed and the maintenance cost may become low. Although the sensor module is supplied with a power source, for the reasons described above, it is difficult to provide a wire that supplies a power source to the sensor module, and therefore a battery is arranged in the sensor module, and it is desirable that the sensor module may be used for a long period of time without performing maintenance, such as exchange of batteries.
As described above, a sensor system that is easily attached and which is not maintained, such as exchange of batteries, for a long period of time has not been implemented.